The invention relates to a vehicle brake system which comprises a motor/pump unit with an electromotor and at least one pump for delivering brake fluid. The electromotor comprises a motor stator in which a motor rotor is rotatably disposed. The pump is disposed substantially within the motor rotor and can be driven by the latter. The invention also relates to a motor/pump unit of this kind.
The motor/pump unit serves to deliver brake fluid to and from wheel brakes of the vehicle brake system in order to actuate or release these brakes. Vehicle brake systems of this kind are also called electrohydraulic brake systems, which can be operated in so-called anti-lock braking, traction or vehicle movement dynamics control mode. The motor/pump unit may be disposed directly at a wheel brake of a vehicle or serve as a central supply member for a plurality of wheel brakes.
A brake system with a vehicle brake actuator in which an electromotor comprises a stator winding fitted in a stationary fashion and a rotor fitted so as to be rotatable therein is known from U.S. Pat. No. 4,435,021 A, which is hereby incorporated by reference. The rotor bears a plurality of axial pistons which are supported at an inclined end face, with which they form an inclined-plate pump. Brake fluid which flows around the rotor emerges at the axial pistons during operation of the inclined-plate pump. The brake fluid also enters a gap between the stator winding and the rotor, where it gives rise to a high fluid friction resistance and reduces the magnetic flux between the stator winding and the rotor. The electromotor therefore has a low dynamic performance level, i.e. poor starting and response characteristics.
The object of the invention is to remedy the above-mentioned problem and in particular to provide a vehicle brake system with a motor/pump unit which is capable of delivering brake fluid in a highly dynamic fashion.
The object is achieved according to the invention by a vehicle brake system with a motor/pump unit which has the above-mentioned features and is developed such that the motor stator and at least one section of the motor rotor which is directed towards the motor stator define an electromagnetic region, at least the pump defines a hydraulic region, and at least one sealing element is provided which separates the electromagnetic region from the hydraulic region in a fluid-tight fashion.
The sealing element which is disposed according to the invention separates the motor stator and the section of the motor rotor which faces it from the hydraulic region of the pump, in which brake fluid is located. It is therefore impossible for any brake fluid to enter the gap between the motor stator and the motor rotor. This means that no fluid friction resistance occurs in the gap and the dynamic performance of the electromotor is significantly augmented. This measure at the same time increases the efficiency of the electromotor. The result is a an electromotor and pump combination which is optimised in control terms. Moreover, the electromagnetic region is separated from the hydraulic region in a fluid-tight fashion, so that no dirt can reach the electromagnetic region. There is thus no possibility of the motor stator being soiled or damaged, for example due to aggressive brake fluid. The electromotor and the pump are in this case of a particularly compact configuration in a so-called cartridge construction. It is also possible for a plurality of pumps to be surrounded by the motor rotor, in particular radially, in order, for example, to provide an individual pressure source for each wheel brake.
The object is also achieved according to the invention by a motor/pump unit of this kind.
The vehicle brake system is advantageously developed such that there is just an air gap between the motor stator and the motor rotor. The entire motor rotor is located in the hydraulic region in the case of the vehicle brake actuator which is described in U.S. Pat. No. 4,435,021 A. The motor winding is therefore surrounded internally by a partition which separates it off from the hydraulic region and also from the motor rotor. However this partition may be dispensed with in order to achieve the object according to the invention. The spacing between the motor stator and the motor rotor may therefore be very small. This additionally improves the efficiency and response and starting characteristics of the electromotor.
According to an advantageous development, the motor stator is fitted in a stationary fashion in a casing, and the sealing element is formed in an annular fashion between the motor rotor and the casing. In this particularly simple configuration of the invention the sealing element which is used may be a conventional, inexpensive sealing ring which is selected from a wide range and can therefore be adapted particularly well to the sealing object which is to be achieved.
In an advantageously developed vehicle brake system the motor rotor is rotatably supported in the casing about a rotational axis by means of two bearings which are disposed at the axial end regions of the motor rotor. The bearings enable the motor rotor to be precisely guided, with the possibility of adjusting its position independently of the pump.
The motor rotor is advantageously substantially cup-shaped and comprises at its bottom a coaxially fitted drive shaft, which is connected in a driving fashion, for driving the pump. Because the cup shape is only open to one side, a configuration of this kind enables a closed space for the pump to be sealed off particularly easily in the motor rotor. For example, a sealing element may be disposed at the opening of the cup-shaped motor rotor for this purpose.
However the casing advantageously comprises a substantially hollow cylindrical casing section which projects radially inwards and coaxially into the cup-shaped motor rotor, and the sealing element is advantageously disposed between the hollow cylindrical casing section and the drive shaft. The motor rotor is thereby sealed off at a relatively small area, and a sealing element of a small diameter can be used. Sealing elements of this kind have a relatively low frictional resistance and require little construction space. Moreover, because the casing section is disposed between the motor rotor and the pump, there is no fluid friction between the motor rotor and the pump.
In an advantageous configuration the motor rotor is substantially of a hollow cylindrical shape and connected in a driving fashion to the pump at an inner circumferential surface. This constitutes a particularly simple coupling between the pump and the motor rotor which may, for example, be in the form of a tongue-and-groove joint. The motor rotor and the pump may in this respect be elastically connected such that little structure-borne sound is transmitted outwards from the pump to the motor rotor and the casing.
A respective sealing element is advantageously disposed between the axial end sections of the motor rotor and the casing in this configuration. This means that a particularly large construction space is available for the pump. The pump may also pass axially through the motor rotor.
The pump is advantageously formed as an inclined-plate pump, in which a pump rotor is coupled in a driving fashion to the motor rotor, in which pump rotor at least one axial piston can be displaced, the latter being supported at an inclined plate fitted in a stationary fashion to the casing. This configuration is used together with a hollow cylindrical motor rotor, to which the pump rotor is directly coupled. The pump rotor may then also be integral with the motor rotor.
The pump may alternatively be in the form of a swash-plate pump, with a swash plate being coupled in a driving fashion to the motor rotor and supporting at least one axial piston which can be axially displaced in a piston guide which is fitted in a stationary fashion to the casing. This configuration can be used to particular advantage together with a cup-shaped motor rotor, to the bottom of which the swash plate is coupled.